According to a dynamic speaker, a voice coil bobbin around which a voice coil is wound is basically mounted on an inner peripheral edge of a conical diaphragm, an outer peripheral edge of the diaphragm is mounted on a frame through an edge portion, and the voice coil bobbin is mounted on the frame through a damper. That is, the edge portion and the damper constitute a suspension of a vibration body such as the diaphragm or the voice coil bobbin.
For example in a speaker for reproducing deep bass called woofer or subwoofer which is utilized in an audio system for a vehicle, since a diameter of the diaphragm is limited, a large amplitude stroke of the diaphragm is secured so that sufficient sound pressure level in bass can be secured.
Especially a damper constituting a suspension of the vibration body must have a function for securing an amplitude stroke of the same level as that of the edge portion while avoiding contact of the voice coil with a pole piece or a yoke constituting a magnetic gap.
Therefore, it is difficult to provide the damper with large compliance, and there is a problem that in a damper of the speaker which secures a large amplitude stroke, a non-linear movable load is provided and power linearity is deteriorated. In addition, there is also a problem that mechanical fatigue of the damper occurs faster than the edge portion.
To secure compliance of the damper, a corrugation damper having a corrugated cross section shape is widely used, but there is a problem that peculiar vibration and scratchy sound and the like are generated by deformation of between corrugating adjoined by amplitude motion. This phenomenon remarkably occurs in a speaker having a large amplitude stroke of the diaphragm.
Hence, the present applicant has already filed an application of a speaker device in which for example, a roll-type edge having the same function as that of the edge portion is employed instead of the damper, and rigidity of the diaphragm in the vibration direction can be enhanced. This is disclosed in a publication of unexamined application indicated as Patent Document 1.
According to a structure of the speaker disclosed in Patent Document 1, the problem generated when the damper is used can be solved, and rigidity of the diaphragm in the vibration direction can be enhanced and thus, excellent acoustic feature can be obtained as a bass reproducing speaker.
Patent Document 1: Japanese Patent Application Laid-Open No. 2005-191746